Effects of combined chlorine on physicochemical properties and structure of shellac.

The objective of this work was studying the effects of combined chlorine on the physicochemical properties and the structure of shellac. Bleached shellacs with different chlorine content were prepared by means of elimination reaction which sodium ethoxide was used as nucleophilic reagent. Then polymerization time and iodine value characterizing the quality of shellac were tested for investigating the relationship between the physicochemical properties and chlorine. The mechanism of dechlorination of shellac was analyzed, and the structures of products were characterized with the aid of ultraviolet spectrophotometer. It was demonstrated that the polymerization time become long and the value of double bond become large with the decrease of chlorine combined in shellac molecule, and that the properties of shellac with low chlorine content had been improved. The structure of shellac obtained by means of dechlorination was different from that of product without dechlorination.